U.S. patent application number 14/787970 was filed with the patent office on 2016-03-31 for aluminum spot welding method.
The applicant listed for this patent is MAGNA INTERNATONAL INC.. Invention is credited to TERENCE ANTHONY DEVERS, JOHN EDWARD HILL.
Application Number | 20160089745 14/787970 |
Document ID | / |
Family ID | 51843944 |
Filed Date | 2016-03-31 |
United States Patent
Application |
20160089745 |
Kind Code |
A1 |
HILL; JOHN EDWARD ; et
al. |
March 31, 2016 |
ALUMINUM SPOT WELDING METHOD
Abstract
A welding tip (20) for spot welding a first part (22) formed of
conductive metal, for example aluminum, to a second part (24)
formed of aluminum or another conductive metal, such as steel, is
provided. The welding tip (20) includes a notch (30) at a distal
end (38) and a convex contact surface (28) extending radially
outwardly and upwardly from the notch (30) for engaging a surface
of the first part (22). The rotating welding tip (20) forms a
depression (32) on the surface of the first part (22) during the
welding process. The notch (30) creates a pin (34) in the center of
the depression (32) which provides a fixed axis of rotation for the
rotating welding tip (20) and prevents the welding tip (20) from
moving radially relative to the fixed axis, thereby improving the
quality of the final spot weld (36) and reducing process time.
Inventors: |
HILL; JOHN EDWARD; (Shelby
Township, MI) ; DEVERS; TERENCE ANTHONY; (London,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MAGNA INTERNATONAL INC. |
Aurora |
|
CA |
|
|
Family ID: |
51843944 |
Appl. No.: |
14/787970 |
Filed: |
May 1, 2014 |
PCT Filed: |
May 1, 2014 |
PCT NO: |
PCT/US14/36333 |
371 Date: |
October 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61819182 |
May 3, 2013 |
|
|
|
Current U.S.
Class: |
403/271 ;
219/86.1; 219/91.2 |
Current CPC
Class: |
B23K 35/0255 20130101;
B32B 15/016 20130101; B23K 11/115 20130101; B32B 15/01 20130101;
B23K 11/24 20130101; B23K 11/3009 20130101; B23K 11/04 20130101;
B23K 2103/10 20180801 |
International
Class: |
B23K 11/11 20060101
B23K011/11; B23K 11/04 20060101 B23K011/04; B23K 11/24 20060101
B23K011/24 |
Claims
1. A welding tip for spot welding parts formed of conductive metal,
comprising: a shaft extending to a distal end and presenting a
notch at said distal end; and said shaft including a contact
surface extending radially outwardly from said notch.
2. The welding tip of claim 1, wherein a cross-sectional area of
said contact surface is greater than a cross-sectional area of said
notch.
3. The welding tip of claim 1, wherein said contact surface is a
convex surface extending upwardly from said notch; and said notch
is located at an apex of said convex contact surface.
4. The welding tip of claim 1, wherein said shaft is formed of
conductive metal.
5. A method for spot welding parts formed of conductive metal,
comprising the steps of: providing a first part formed of
conductive metal and a second part formed of conductive metal;
contacting the first part with a first welding tip while rotating
the first welding tip around its center axis, the first welding tip
including a shaft extending to a distal end and presenting a notch
at said distal end, and the shaft including contact surface
extending radially outwardly from the notch.
6. The method of claim 5, wherein the rotating step includes
forming a depression and a pin extending upwardly from the
depression in the first part; and rotating the first welding tip
about the pin.
7. The method of claim 6, wherein the notch and the pin fix the
axis of rotation of the first welding tip during the rotating step
and prevent the first welding tip from moving radially relative to
the fixed axis during the rotating step.
8. The method of claim 5, wherein at least one of the first part
and the second part is formed of aluminum or an aluminum alloy.
9. The method of claim 5 including applying electrical current to
the first welding tip during the step of contacting the first part
while rotating the first welding tip.
10. The method of claim 5 including applying no current to the
first welding tip for a first period of time; rotating the first
welding tip before contacting the first part with the first welding
tip during the first period of time; and applying force to the
first part by the first welding tip during the first period of
time.
11. The method of claim 10 including contacting a spot on the first
part during the first period of time and during a second period of
time immediately following the first period of time; applying
electrical current to the first welding tip during the second
period of time; melting the first part in the spot during the
second period of time; decreasing the force applied to the first
part by the first welding tip during the second period of time;
contacting the spot on the first part during a third period of time
immediately following the second period of time; increasing the
electrical current applied to the first welding tip while rotating
the first welding tip during the third period of time; the rotating
steps including continuously or intermittently rotating the first
welding tip around its center axis and forming a depression in the
first part and a pin extending upwardly from the depression; and
rotating the first welding tip about the pin, wherein the pin locks
the first welding tip to the first part and prevents the first
welding tip from moving radially relative to its center axis during
the rotating step.
12. The method of claim 11 including providing no electrical
current to the first welding tip while increasing the force applied
to the first part by the first welding tip and optionally rotating
the first welding tip during a fourth period of time immediately
following the third period of time.
13. The method of claim 12 including allowing the first part to
cool while still contacting the first part with the first welding
tip after the third period of time by applying no electrical
current to the first welding tip; and rotating the first welding
tip less than 360 degrees around its center axis in a first
direction and rotating the first welding tip less than 360 degrees
around its axis in a second direction opposite the first direction
while allowing the first part to cool and while contacting the
first part with the first welding tip.
14. The method of claim 5, wherein a cross-sectional area of the
contact surface of the first welding tip is a convex surface
extending upwardly from the notch, and the notch is located at an
apex of the convex contact surface.
15. The method of claim 5 including contacting the second part with
a second welding tip while contacting the first part with the first
welding tip; and rotating the second welding tip around its center
axis while rotating the first welding tip around its center axis,
the second welding tip including a shaft extending to a distal end
and presenting a contact surface around the distal end, and the
shaft presenting a notch at the distal end.
16. The method of claim 15, wherein the center axis of the first
welding tip is aligned with the center axis of the second welding
tip during the step of rotating the second welding tip around its
center axis while rotating the first welding tip around its center
axis.
17. The method of claim 15 including applying no current to the
second welding tip for a first period of time; rotating the second
welding tip before contacting the second part with the second
welding tip during the first period of time; and applying force to
the second part by the second welding tip during the first period
of time.
18. A spot welded structure, comprising: a first part formed of
conductive metal joined to a second part formed of conductive metal
by a spot weld, wherein the spot weld comprises a depression and a
pin extending upwardly from the depression on at least one of the
first part and the second part.
19. The spot welded structure of claim 19, wherein the depression
includes a concave surface and the pin extends upwardly from the
concave surface.
20. The spot welded structure of claim 18, wherein the spot weld
includes a first depression and a first pin on the first part and a
second depression and a second pin on the second part, and the
first depression is axially aligned with the second depression.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This U.S. National Stage Patent Application claims the
benefit of PCT International Patent Application Ser. No.
PCT/US2014/036333 filed May 1, 2014 entitled "Aluminum Spot Welding
Method," which claims the benefit of U.S. Provisional Patent
Application Ser. No. 61/819,182 filed May 3, 2013, entitled
"Aluminum Spot Welding Method," the entire disclosures of the
applications being considered part of the disclosure of this
application and hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to spot welding methods,
tools used for spot welding, and parts joined by spot welding.
[0004] 2. Related Art
[0005] Spot welding is oftentimes used to join a first part formed
of aluminum to a second part formed of aluminum or another metal
material. The parts are held together under pressure by a pair of
welding tips, which also function as electrodes. Current is
supplied to the welding tips and concentrated in a single spot to
melt the surface and form the weld. One drawback of spot welding
aluminum parts is that aluminum oxides typically form along the
surfaces, which reduces the integrity of the weld.
[0006] To break the oxide surface and reduce the amount of aluminum
oxides formed during spot welding, the welding tips can present a
spherical radius at their terminal end, and rotate continuously or
intermittently at a controlled rate as they spot weld the parts
together. An example of this technique was developed by KUKA and
Mercedes-Benz.RTM. and is referred to as robo-spinning. The
robo-spinning technique uses a robot to rotate the welding tips and
spot weld the parts together. However, due to the significant force
applied and the shape of the part being welded, the rotating weld
tips tend to move out of position during the spot welding process.
In addition, the terminal ends of the rotating welding tips can
melt the surfaces of the parts and create locking divots.
SUMMARY OF THE INVENTION
[0007] The invention provides a welding tip for spot welding parts
formed of conductive metal, such as aluminum. The welding tip
comprises a shaft extending to a distal end and presenting a notch
at the distal end. The shaft also includes a contact surface
extending radially outwardly from the notch.
[0008] The invention also provides a method for spot welding. The
method includes providing a first part formed of conductive metal
and a second part formed of conductive metal. The method then
includes contacting the first part with the welding tip while
rotating the welding tip around its center axis.
[0009] The invention further provides a spot welded structure
formed using the welding tip. The spot welded structure comprises
the first part formed of conductive metal joined to the second part
formed of conductive metal by a spot weld. The spot weld comprises
a depression and a pin extending upwardly from the depression.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Other advantages of the present invention will be readily
appreciated, as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0011] FIG. 1 is a side cross-sectional view of a welding tip
according to an example embodiment of the invention;
[0012] FIG. 2 is a bottom view of the welding tip of FIG. 1;
[0013] FIG. 3 is a chart illustrating phases of a spot welding
process according to an example embodiment;
[0014] FIG. 4 illustrates a pair of welding tips spot welding a
first part to a second part according to an example embodiment;
[0015] FIG. 5 illustrates a structure including a first part spot
welded to a second part according to an example embodiment; and
[0016] FIG. 6 shows the top and bottom of the spot welded structure
of FIG. 5.
DETAILED DESCRIPTION
[0017] The invention provides a welding tip 20, as shown in FIGS. 1
and 2, for spot welding a first part 22 formed of conductive metal,
typically aluminum, to a second part 24 formed of conductive metal,
such as aluminum or another metal. The spot welding process is
preferably a robo-spin or electromechanical motion spin process,
for example the process illustrated in FIGS. 3 and 4, wherein the
welding tip 20 rotates around its center axis A either continuously
or intermittently. A high quality spot welded structure 25
including the first part 22 joined to the second part 24 by a spot
weld 36, such as the structure 25 shown in FIGS. 5 and 6, can be
formed by the method of the present invention. The welding tip 20
and method of the present invention can also avoid forming divots
along the surface of the parts 22, 24, which are often formed by
traditional spot welding tips. The welding tip 20 can also reduce
the total spot welding process time. More specifically, the time it
takes to fix the rotating welding tip 20 to one of the parts 22, 24
is reduced. In addition, the welding tip 20 requires less
electrical current during the spot welding process, compared to a
traditional welding tip.
[0018] The welding tip 20 may be formed of a copper alloy or
another electrically conductive material so that when the welding
tip 20 receives an electrical current the welding tip 20 functions
as an electrode. The welding tip 20 of FIG. 1 is uncoated, but the
welding tip 20 may alternatively be coated to reduce friction while
rotating around its center axis A and thus experience less
wear.
[0019] The welding tip 20 includes a shaft 26 which is typically
disposed in a spot welding gun (not shown). The shaft 26 extends
along the center axis A to a distal end 38 and includes a notch 30
at the distal end 38. A contact surface 28 surrounds the notch 30
at the distal end 38 for engaging the parts 22, 24 to be welded. As
shown in FIGS. 1 and 2, the contact surface 28 extends radially
outwardly and upwardly from the notch 30. The contact surface 28
also has a spherical radius which provides a rounded surface
adjacent the distal end 38. In the example embodiment, the contact
surface 28 presents a convex or semi-spherical shape. The area of
the contact surface 28 and the size of the spherical radius can
vary, depending on certain parameters, including, but not limited
to, the thickness of the parts 22, 24 to be joined. Alternatively,
other shapes may be used instead of the convex surface, depending
on the desired formation of the spot weld 36 to be formed.
[0020] In the example embodiment of FIG. 1, the shaft 26 includes a
slot 27 extending along the center axis A for receiving another
component of the welding gun (not shown) which conveys the
electrical current to the welding tip 20 during the welding
process. The end of the slot 27 is spaced axially from the contact
surface 28 of the spot welding tip 20.
[0021] The notch 30 of the welding tip 20, also referred to as a
cavity, dimple, depression, or arbor, reduces the area of the
surface in contact with one of the parts 22, 24. As a result, of
the reduced area, the welding tip 20 requires less electrical
current during the spot welding process, compared to a traditional
welding tip. The notch 30 is preferably located at an apex of the
convex contact surface 28 and extends inwardly along the center
axis A away from the distal end 38, as shown in FIGS. 1 and 2. The
cross-section of the notch 30 typically has a circular shape, as
shown in FIG. 2, but can comprise other shapes. The diameter
D.sub.1 of the notch 30 can vary depending on the size of the
contact surface 28 and the parts 22, 24 to be joined, or other
factors. However, the cross-sectional area of the contact surface
28 surrounding the notch 30 is typically greater than the
cross-sectional area of the notch 30, as shown in FIG. 2.
[0022] The depth d.sub.1 of the notch 30 can also vary depending on
the size of the shaft 26 and parts 22, 24 to be joined, or other
factors. In the example embodiment of FIG. 1, the depth d.sub.1 of
the notch 30 is contained within the spherical portion of the
welding tip 20 and is spaced from the slot 27 which receives the
component of the welding gun. For example, the depth d.sub.1 of the
notch 30 could be less than 30 percent (%), or less than 20%, or
less than 10%, or less than 5% of the distance between the distal
end 38 of the welding tip 20 and the slot 27 for receiving the
welding gun. The depth d.sub.1 of the notch 30 could also be less
than 10%, or less than 5%, or less than 1% of the total length 1 of
the welding tip 20.
[0023] During the spot welding process, the contact surface 28 of
the rotating welding tip 20 forms a depression 32 on the surface of
one of the parts 22, 24 to be joined. As the contact surface 28
forms the depression 32, the notch 30 creates a pin 34 extending
upwardly from the center of the depression 32. The notch 30 fixes
or secures the welding tip 20 to the surface of one of the parts
22, 24, and the pin 34 provides a fixed axis of rotation for the
welding tip 20. The pin 34 also prevents the welding tip 20 from
moving radially relative to the center axis A while rotating around
the center axis A. The notch 30 also allows for precise location of
applied force and electrical current which further prevents the
rotating welding tip 20 from moving out of position. As alluded to
above, the notched welding tip 20 has much higher electrode force
density and requires less initial electrical current during the
welding process--compared to a traditional welding tip, since the
contact surface 28 is reduced. The depression 32 and pin 34 remain
on the final spot welded structure 25 as a witness to the process
quality. It can be measured as a quality indicator relating to
roundness in shape and surface indentation depth.
[0024] The invention also provides a method for joining the first
part 22 formed of conductive metal to the second part 24 formed of
conductive material by a spot welding method using the notched
welding tip 20 and thus forming the spot welded structure 25. The
method preferably includes the robo-spinning technique, but can
comprise another method that involves rotating the welding tip 20
around its center axis A, either continuously or intermittently.
FIG. 3 illustrates phases of an example method used to spot weld
the parts 22, 24, including the degree of force F, electrical
current I, and electrical resistance R applied during each phase of
the spot welding process.
[0025] The method begins by providing the first part 22 and the
second part 24 to be welded. The first part 22 is formed of
conductive metal, such as aluminum, and the second part 24 is also
formed of conductive metal, which is typically aluminum, but may be
another conductive metal, such as steel. The size and shape of the
parts 22, 24 can vary depending on the intended application of the
finished spot welded structure 25. For example, the parts 22, 24
can be designed for use as a component of an automotive vehicle. In
addition, the parts 22, 24 can be pre-conditioned in any manner
know in the art to improve the integrity of the spot weld 36
ultimately joining the parts 22, 24. The conductive metal of the
parts 22, 24 can also be coated or uncoated. Coating thicknesses
are becoming increasingly thicker to cope with corrosion issues.
Example coatings include aluminum, zinc, and combinations of alloys
to protect the conductive metal from corrosion.
[0026] Typically, the method employs two of the notched welding
tips 20, including the first welding tip 20 and a second welding
tip 20', as shown in FIG. 4. A pair of welding guns (not shown)
each including one of the notched welding tips 20, 20' are used to
spot weld 36 the parts 22, 24. As shown in FIG. 4, the first and
second welding tips 20, 20' are aligned on opposite sides of the
parts 22, 24 to be joined. The welding tips 20, 20' preferably have
the same design and perform the same function at the same time. For
example, the first welding tip 20 engages the first part 22 while
the second welding tip 20' engages the second part 24, or vice
versa. Accordingly, although the following description refers to
only the first welding tip 20 and the first part 22 in several
instances, the description also applies to the second welding tip
20' and the second part 24.
[0027] The method begins with a first phase including supplying
power to the welding gun, which drives the welding tip 20 to rotate
around its center axis A, preferably before contacting the part 22.
In the example embodiment, the rotating step begins before the
welding tip 20 contacts the surface of the part 22 in order to
reduce process time. The first phase of the example spot welding
process also includes crimping the parts 22, 24 before any
electrical current I or heat is applied to the welding tips 20, 20'
or the parts 22, 24. This cold crimping first phase can be applied
in any situation, but is typically applied when a gap between the
parts 22, 24 is present, for example, due to manufacturing
tolerances. The first phase comprises a first period of time at the
start of the welding process, during which the rotating welding
tips 20, 20' first contact a spot along the surface of each of the
parts 22, 24. As shown in FIG. 3, no electrical current I is
applied to the welding tips 20, 20' during the first phase. Once
the rotating welding tips 20, 20' contact the parts 22, 24, the
first phase includes applying a significant force F to the parts
22, 24 by the welding tips 20, 20'. The center axis A of the first
welding tip 20 is aligned with the center axis A' of the second
welding tip 20', as shown in FIG. 4, as the welding tips 20, 20'
rotate.
[0028] The welding tip 20 can rotate continuously or intermittently
during the first phase. As the rotating welding tip 20 develops
force, any oxide layer present on the surface of the part 22 is
removed. The rotating welding tip 20 can also score, remove,
condition, or scrub any coating on the surface of the part 22. At
the end of the first phase, the force F applied to the welding tip
20 is typically reduced in preparation for the second phase.
[0029] The second phase of the example method shown in FIG. 3
includes softening the part 22. During the second phase, which is a
second period of time immediately following the first period of
time, the force F is still applied to the rotating welding tip 20
at a constant level. The electrical current I is then turned on and
applied to the welding tip 20 in order to soften the part 22. FIG.
3 shows that the electrical current I initially increases and then
stays at a constant level throughout the second phase, while the
electrical resistance R is highest at the beginning of the second
phase and decreases continuously throughout the second phase.
[0030] The temperature of the part 22 also increases during the
second phase as the welding tip 20 continues to rotate while in
contact with the part 22. Thus, the spot along the surface of the
part 22 engaged by the rotating welding tip 20 begins to melt, and
the welding tip 20 begins forming the depression 32 and the pin 34
extending upwardly from the center of the depression 32. Once the
pin 34 forms, the welding tip 20 rotates about the pin 34. The
notch 30 and pin 34 fix the axis of rotation at the center axis A
of the welding tip 20 and prevent the welding tip 20 from moving
radially relative to the center axis A during the rotating step. In
other words, the notch 30 and pin 34 fix or secure the welding tip
20 to the part 22 and prevent the welding tip 20 from moving or
shifting radially relative to its center axis A during the rotating
step of the second phase.
[0031] The welding tip 20 can rotate continuously or intermittently
during the second phase. In either case, the welding tip 20 rotates
quickly enough to prevent the melted aluminum or other conductive
metal of the part 22 from sticking to the contact surface 28 or
notch 30 of the welding tip 20. The lack of oxides on the surface
of the part 22 also prevents the melted metal from sticking. Thus,
the service life of the welding tip 22 is improved.
[0032] The third phase of the example method shown in FIG. 3 is the
welding phase. During the third phase, which is a third period of
time immediately following the second period of time, the force F
is maintained at the same level as in the second softening phase.
However, the electrical current I increases sharply to its highest
level and stays at that level during the majority of the third
phase, while the electrical resistance R continues to slowly
decrease. As the welding tip 20 continues rotating, the temperature
continues to increase and the spot along the surface of the part 22
continues to melt. During the third phase, the notch 30 continues
to fix the welding tip 20 to the surface of the part 22, while the
pin 34 provides the fixed center axis A of rotation for the
rotating welding tip 20. Thus, the notch 30 allows for precise
location of the applied force F and electrical current I, which
leads to a higher quality spot weld 36 in the finished structure
25. The notch 30 also continues to prevent the welding tip 20 from
moving, sliding, or skidding out of position. Towards the end of
the third phase, the spot weld 36, also referred to as a weld
nugget is typically formed between the two parts 22, 24. At the end
of the third phase, the electrical current I is sharply reduced to
zero, the electrical resistance R is gradually reduced to zero, and
the temperature of the welding tip 20 and the part 22 begins to
decrease. Thus, the part 22 begins to cool at the end of the third
phase and after the third phase.
[0033] In the example embodiment shown in FIG. 3, the fourth phase
includes forging. The forging is beneficial to reduce cracking
along the surface of the part 22, especially when the part 22 is
formed of an alloy, but the forging step is not required. During
the optional fourth phase, which is a fourth period of time
immediately following the third period of time, the electrical
current I is turned off, and the welding tip 20 and part 22
continue to cool. The force F applied to the part 22 by the welding
tip 20 during the fourth phase increases relative to the second and
third phases. The force F applied during the fourth phase is
approximately equal to, or at least equal to the force F applied
during the first phase, and the force F remains at this high level
for a majority of the fourth phase. A high capacity welding gun may
be required to achieve this high level of force F during the first
and fourth phases. In addition, the welding tip 20 can optionally
rotate during the fourth phase.
[0034] The welding tip 20 typically stops rotating continuously
around its center axis A at some point after the third phase. If
the method includes the optional fourth phase, then the welding tip
20 stops rotating continuously before, during, or after the fourth
phase. A cooling phase (not shown in FIG. 3) then begins either
after the third phase or after the optional fourth phase, wherein
the depressions 32 and pin 30 formed by the welding tip 20 can
solidify and provide the finished spot weld 36 joining the first
part 22 and the second part 24. At the beginning of the cooling
phase, the welding tip 20 is still in contact with the part 22, and
the method preferably includes "swiveling" or rotating the welding
tip 20 less than 360 degrees around its center axis A in a first
direction, and preferably followed by rotating the welding tip 20
less than 360 degrees around its center axis A in a second
direction opposite the first direction. For example, the swiveling
step can include rotating 10 degrees in one direction, or rotating
5 degrees clockwise followed by 5 degrees counterclockwise. This
swiveling step further prevents the aluminum or other conductive
metal from sticking to the welding tip 20. The swiveling motion can
be repeated a plurality of times, either continuously or
intermittently. The swiveling step can also be incorporated into
other phases of the spot welding process. The pin 34 formed on the
surface of the part 22 remains disposed in the notch 30 of the
welding tip 20 during the swiveling step and keeps the welding tip
20 in position during the swiveling step.
[0035] The invention further provides a structure 25 including the
first part 22 formed of aluminum and the second part 24 formed of
aluminum or another metal material joined together by the spot weld
36, as shown in FIGS. 5 and 6. The spot weld 36 comprises the
depression 32 on the surface of each part 22, 24, and the pin 34
extending upwardly from the center of each depression 32. The
depression 32 typically presents a concave surface and the pin 34
extends upwardly from the center of the concave surface. The pin 34
formed in the first part 22 is preferably aligned with the pin 34
formed in the second part 24. The pin 34 makes it easy to identify
spot welded structures 25 formed using the notched welding tip 20
of the present invention. The depth d.sub.2 and diameter D.sub.2 of
each depression 32 can vary, depending on the size of the welding
tip 20 and the pressures and temperatures of the spot welding
process. However, the total cross-sectional area of each depression
32 is typically greater than the total cross-sectional area of each
pin 34, as shown in FIG. 5. The spot weld 36 formed using the
notched welding tip 20 is higher quality than spot welds formed
using other welding tips without the notch 30.
[0036] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings and may be
practiced otherwise than as specifically described while within the
scope of the claims.
* * * * *